France’s far-right National Front (FN) came under scrutiny for possible financial irregularities on Monday after the European Parliament alerted anti-fraud investigators to the party’s use of funds to pay EU parliamentary assistants.

The European Parliament issued a statement announcing that its president, Martin Schulz, had informed the European Anti-Fraud Office (OLAF) of the suspected irregularities regarding the salaries of EU parliamentary assistants, which are paid out of the EU’s budget.

The parliament suspects 20 assistants of actually working for the FN in France instead of for EU lawmakers.

Assistants must work “directly” for lawmakers, the parliament stressed in its statement, meaning that they are not allowed to work for national parties.

A parliamentary source said the suspected fraud was estimated at 7.5 million euros ($8.1 million), confirming figures given by French daily newspaper Le Monde.

Schulz also wrote to French Justice Minister Christiane Taubira to express his suspicions.

Marine Le Pen, leader of the FN, quickly took to Twitter to respond, announcing that she intended to file a complaint over the "false accusation".

"Basically, Schulz is right... our assistants do not work for the European Union but against it," he tweeted, underlining his party's fierce opposition to the EU.

OLAF must now decide whether or not to open an investigation, a process which could take several months.

The controversy comes as the FN prepares for local elections in France on March 22 and 29. The party has made steady gains over the past year, winning a record 23 seats in European elections in 2014. It is also projected to win an “unprecedented” score in France’s upcoming vote.

French Prime Minister Manuel Valls warned on Sunday that the FN could take the next presidential election in 2017, saying their policies were a "disaster" for the country.